The invention relates to compositions and methods for increasing the survival of neurons.
The growth, survival, and differentiation of neurons in the peripheral and central nervous systems (PNS and CNS, respectively) are dependent, in part, on target-derived, paracrine, and autocrine neurotrophic factors. Conversely, the lack of neurotrophic factors is thought to play a role in the etiology of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease). In neuronal cell cultures, neurotrophic support is provided by co-culturing with astrocytes or by providing conditioned medium (CM) prepared from astrocytes. Astrocytes of ventral mesencephalic origin exert much greater efficacy in promoting the survival of ventral, mesencephalic dopaminergic neurons, compared with astrocytes from other regions of the CNS, such as the neostriatum and cerebral cortex. In chronic, mesencephalic cultures of 21 days in vitro (DIV) or longer, the percentage of dopaminergic neurons increases from 20% to 60%, coincident with proliferation of a monolayer of astrocytes. In contrast, in conditions in which the proliferation of astrocytes was inhibited, dopaminergic, but not GABAergic neurons, were almost eliminated from the cultures by 5 DIV. These results demonstrate the importance of homotypically-derived astrocytes for the survival and development of adjacent dopaminergic neurons, and suggest that mesencephalic astrocytes are a likely source of a physiological, paracrine neurotrophic factor for mesencephalic dopaminergic neurons.
The repeated demonstration that astrocytes secrete molecules that promote neuronal survival has made astrocytes a focus in the search for therapeutics to treat neurodegenerative diseases. Many laboratories have attempted to isolate astrocyte-derived neurotrophic factors, but have been hindered by a major technical problem: serum is an essential component of the medium for the optimal growth of primary astrocytes in culture, yet the presence of serum interferes with the subsequent purification of factors secreted into the conditioned medium.
Thus, there is a need to identify and purify new neurotrophic factors and to identify new methods to produce conditioned medium that are compatible with protein isolation techniques.